Neurons contact each other mostly by synaptic transmission at synapses. Synaptic transmission relies on vesicle exocytosis, i.e., fusion of vesicles with the plasma membrane and release of transmission. To maintain vesicle exocytosis, fused vesicles must be retrieved, or endocytosed, to form new vesicles for the second round of exocytosis. My goal is to improve our understanding on the cellular and molecular mechanisms underlying synaptic vesicle exocytosis and endocytosis, which are the building block for synaptic transmission and thus the signaling process in the neuronal network. [unreadable] [unreadable] My progress in the last year is listed in the following. First, we found that calcium triggers rapid endocytosis during intensive stimulation. This finding suggests that calcium-mediated accerelation of endocytosis contributes to the maintenance of synaptic transmission during intensive nerve activity, during which fast vesicle cycling is needed to maintain synaptic transmission (J Neurosci, 2005). Second, we found that quantal size, the most fundamental parameter that determines synaptic strength, is regulated by the glutamate concentration inside the vesicle (submitted to Neuron). Third, we found two modes of fusion, full collapse and kiss and run mode (revised in Nature).